Antenna coupling system



Jan. 1, 1935. J. M. MILLER Q 1,986,641

ANTENNA COUPLING SYSTEM Filed Aug. 2, 1929 INVENTOR $4. M BY mj-gw 4 ATTORNEY invention relates hereductio jn br elimination "of variation of the ant'enna detuning efiectrupona tunable circuitfand which more particularly, is included in a cascaded iseriesi lof resonantncircuit's tunable from resonance at one wave length to resonance at another wave length by like extents of adjustment of their tuning devices, specifically by adjustment of a single control member.

In accordance with my invention, the antenna circuit is tuned to a: wave length higher than all wavelengths to whichthe resonant circuit coupled thereto is tunable; more specifically, a coil is included in the antenna circuit, as in series with the primary of a coupling transformer,

whose reactance is high relative to the reac-- tance of an antenna of usual size for the higher wave lengths to which the resonant circuitsare tunable.

Further in accordance with my invention, the arrangement is utilized with a tunable radio frequency amplifier whose effciency is higher at lower wave lengths to increase the average overall amplification and to effect more substantiallyconstant amplification throughout the wave length range of the amplifier.

My invention further resides in the method and system hereinafter described and claimed.

For an understanding of myinvention reference is made to thenaccompanying drawing in which: g

The figure discloses a receiving system utilizing my invention. T

Referring to the drawing, the thermionic tubes V, V1 and V2 are coupled by the tunable systems comprising the transformers T1, C1 and T2, C2. In the example shown tubes V and V1 are used to, amplify at radio frequency while the tube V2 functions as a detector or demodulator.

The input system of the first tube V of the cascaded series is tunable by condenser C connected across the terminals of the secondary S of the transformer T whose primary P is included in the antenna circuit between the aerial A and earth E. It is characteristic of the system thus far described, that the antenna system affects tuning of the tunable circuit SC so that condenser C in tuning from resonance at one wave length to resonance at another wave length must be adjusted to extents which diifer from the extent of adjustment of the condensers C1 and C2. Further the difi'erence between the condenser settings will vary with changes in the constants of the antenna and for different antennas. Previously, this variation of antenna detuning effect has been minimized by using an antenna coupling transformer of very, high step-up ratioi greatly to reduce the capacity effectively introduced in shunt to the condenser C by connection of the antenna to the primary UNITEDSTATES :B TENT. OFFICE q 1 L I :1,9 s6,s:4;1 ffl f g I I U ING L MJ n 'John:-M.IMiller,' Philadelphia, Pa., assignor to Atwater KcntiManufacturing Company, Phila stigma P a .wr o p bi fene' y a i licatidiinug st 2, 1929?, steam. 382,927

P. 'With this arrangementthe energy transfer ispoorandfbecomes increasingly so as theiapparatus is tuned to the higher wave lengths.

'To" permit like extents of movement 1 ofwthe similar; tuningcondensers C, C1 and C2 when different antennas are used or whenthe antenna constants are varied, intentionally or otherwise, and to insure that when thecondenser rotors are mechanically coupled for movement in unison as by a single dial the circuits are in resonance at the same wave length, there is included in the antenna circuit in series with the primary P of the transformer T a coil L whose reactance is high relative to the reactance of anantenna of usual size for the longest wave length of the band of wave lengths to which the tunable, circuits SC, S1, C2 and S2, C2 are tunable. Otherwise stated the inductance forming a part of the radio apparatus or set to be included in the small number of turns. This arrangement has the undesirable characteristic of decreasing the transfer of energy from the-antenna as the circuits are tuned to the longer wave lengths.

results in marked decrease of overall amplification at the' longer wave lengths particularly as most tuned radio frequency amplifiers are less efiicient at the longer wave lengths.

It is a feature of my invention that the transfer of energy from the antenna to the input circuit of the tube V increases as the wave length increases. This efiect is complementary to the decreasing efficiency of the amplifier at the higher wave lengths resulting in both a higher average amplification and more substantially constant amplification throughout the tuning range of the amplifier. It is desirable that the coil L be of small distributed capacity and resistance. Neither it nor the antenna circuit should have a resonant period within the tuning range.

The value of the inductance coil L may vary within wide limits and depending upon circuit conditions, environment, etc. Its value should be sufliciently high that the antenna system as a whole is tuned to a wave length above the band to which the resonant circuits of the receiving apparatus are tunable. A value of about 2 m. h. was found to be satisfactory for use with an ordinary broadcast receiving set.

The interposition of the inductance L permits the number of turns of the primary P to be increased over the usual number, resulting in better energy transfer. This is possible as the coil L, of definite value, rather than the antenna, circuit, whose values may vary, as with different antennas, determines primarily the detuning effect of the antenna circuit as a whole upon the 1 first tuned circuit. a It will be understood that-the remainder of the circuit may be of any conventional type,the detector V2 supplying current to a translating de-,

vice or to the input of an audio amplifier of one or more stages. The types shown are of the three electrode type and are supplied from a direct current source or battery B. It will be understood, however, that tubes utilizing alternating current for the energization of one or i more electrode circuits may be employed. Other types of tubes, for example, screen grid tubes, may be used.-

. saidtuning devices for adjustment in unison to like extents, an antenna circuit coupled to one ofsaid tunable circuits, and a fixed inductance coilin said antenna, circuit for tuning said antennacircuit to a frequency lower than the lowest frequency of the tuning range of the receiver, said coil having low distributed capacity whereby its natural resonant frequency is at least as high as-the highest frequency of the tuning range of the receiver. 1. a V V I *iJOHN M. MILLER. 

